In-situ combustion process using a surfactant



This invention relates to a process for the recovery of oil from underground mineral oil-bearing formations by thermal means. More particularly, it relates to recovery processes wherein a combustion zone is established and propagated within the formation.

It has previously been proposed to produce oil by the use of underground combustion. In one method a part of the oil or other combustibles within the formation are ignited by suitable thermal means to establish a heat wave or combustion zone at the vicinity of one or more input wells. This heat wave is then usually radially moved to other points in the formation by the injection of a free oxygen-containing gas, such as air, a mixture of oxygencontaining gas and an inert gas, an oxygen-containing gasfuel mixture, etc. As the combustion front moves radially outward the combustion gases, oil and the distillation products migrate in front of the combustion zone to an output well or wells leading from the reservoir, from which output well or wells these fluids are removed and thereafter treated for recovery of the desired valuable constituents. These heated fluids migrating in front of the combustion zone strip the oil bearing sand of the greater portion of oil. The oil remaining is cracked to form a carbonaceous hydrocarbon deposit. Also, as the combustion front moves outward, connate water is vaporized and then condensed at a point further out in the formation where temperatures are lower. Additional Water, which is a product of combustion, is also condensed in this area. The water thus exists in the form of a bank ahead of the heat Wave and is instrumental in producing crude oil by displacement. Again, the crude oil which is not displaced by the water bank remains behind for recovery by the heat wave or to be worked to a carbonaceous material.

This carbonaceous deposit formed in the formation is essentially a fuel for the combustion front and before the front can advance through the formation it is necessary to burn off substantially all the carbonaceous deposit. One of the more important economic factors in thermal recovery processes is the quantity of oxygen-containing gas such as air necessary to move the combustion front through a given volume of reservoir. This quantity of air depends, in turn, upon the quantity of carbonaceous material which must be consumed in order to advance the combustion front. The greater the quantity of residual carbonaceous material left in the formation invaded by the combustion wave, the greater the quantity of oxygen-containing gas that must be supplied under pressure to the input wells to propagate the underground heat wave or combustion zone towards the output wells. The greater the quantity of oxygen needed the greater the cost, for instance compression costs for air are a significant factor in the economic feasibility of the process.

It has now been discovered that the amount of free oxygen-containing gas required to propagate the underground combustion zone can be advantageously reduced by incorporating into the water bank formed ahead of the combustion front a water soluble, preferably relatively oil-insoluble, surface-active or surface tension reducing agent. The incorporation can be accomplished, for instance, by injecting the surface-active agent into the water bank existing ahead of the combustion front, through a bore hole drilled into the area in which the water bank 3,ll5,2@ Patented Dec. 31, 1963 ice exists; or by injecting the surfactant into an oil-bearing formation adjacent an injection well prior to initiation of in-situ combustion from the well. In the latter case, after ignition the surface-active agent migrates along with the heated fluids, i.e. the oil, combustion and distillation products, etc., and when the water bank is formed, solubilizes and remains in the water. The water bank that exists ahead of the thermal front on contact with the crude oil in the porous formation will displace a certain perentage of the oil. Since a relatively high interfacial tension exists at the oil-water contact zone a large percentage of the oil is not ordinarily displaced. The oil remains and is thermally converted to a carbonaceous material which must subsequently be consumed by oxidation. However, in the present invention the presence of the surfactant in the Water bank lowers the interfacial tension at the oil-Water contact thereby increasing the chiciency of the oil displacement by the water bank. Consequently less oil is left behind to be thermally cracked and hence less carbonaceous material, such as coke, is formed, which in turn lowers the quantity of oxygen-containing gas that must be injected to burn through a given volume of reservoir. The in-situ combustion process can be any of the type where the free oxygen-containing gas, combustion wave, water bank and recovered oil are transported from an input to an output well, for instance as in U.S. Patents Nos. 2,642,943; 2,804,146; 2,793,697; 2,670,047; 2,874,- 777 hereby incorporated by reference. It is preferred that the formation in which combustion is being effected be at an elevated pressure, tag. at least about 100 p.s.i.g., and the injected gases contain air and recycled combustion gases from the output well in a proportion to give the desired oxygen content. This type of operation can further reduce gas compression costs.

The surface-active additives that may be used in the present invention are any surface-active agents that are water miscible and preferably relatively oil immiscible. These surface-active agents are usually organic materials containing portions hydrophobic and hydrophilic to each other and include the three recognized classes of surfaceactive agents, that is, the anionic, cationic and nonionic. The preferred surface-active agents for purposes of this invention are those having a good chromatographic transport rate, that is, fast adsorption, and desorption from the stratum or overall low absorptivity into the stratum. The surface active agents possessing a chromatographic transport rate which is at least about of the rate of the water bank travel are preferred.

Sui-table cationic materials for purposes of my invention are amines which include monoamines, diamines and quaternary amines. Examples of these materials which may be mentioned are octadecyl amine, Duomeen T (which has the formula RNH(CH NH in which R represents predominantly a saturated C to C hydrocarbon radical), methyl dodecyl trimethyl ammonium chloride, diisobutyl phenoxy etho-xy ethyl dimethyl benzyl ammonium chloride and tertiary alkyl tetraethoxy ethanolamine. Examples of anionic surfactants are the higher fatty acids such as lauric and stearic acids; the sulfonates such as sulfonated castor oil, alkylated aromatic sulfonates, for instance, sodium octyl naphthalene sulfonate; the sulfates such as the sulfate of oleyl alcohol, alkyl sulfates, alkali metal salts of alkyl aryl polyether sulfates, etc.

Exemplary nonionic agents are those obtained by reaction of hydrophobic hydroxy compounds such as a phenol or alcohol with several moles of an alkylene oxide principally ethylene oxide or propylene oxide. Similarly alkylene oxide reaction products of higher fatty acids are well known as well as of fatty acid esters, including ethylene oxide reaction products of fatty acid esters of anhydrosorbitals. Laurie, palmitic, oleic and stearic acids are commonly used for such esters which may generally be referred to as polyoxyalkylene derivatives of hexitol anhydride partial long chain fatty acid esters, such as polyoxyalliylene sorbitan monostearate. Other nonionic agents include phosphoric acid esters of polyethylene glycol; low-order condensation products of polyhydric alcohols with polybasic water-soluble acids such as glycol tartrate, glycerol citrate, esterificd with stearic acid; high er fatty acid reaction products with alkylolarnines, such as coconut fatty acids with diethanolamine, saponins, etc. various other water miscible surface active agents can be used including, for instance, those in US. Patents Nos. 2,792,894; 2,800,962; 2,875,831 and 2,852,077; 1,894,759; 2,802,785; 2,808,109; 2,812,817; 2,843,545; 2,846,012; 2,882,973 hereby incorporated by reference.

Of the above classes of surface-active agents, the nonionics are preferred for they offer less chance of reacting with the formation. Particularly preferred are the nonionic agents known commercially as the Pluronics which are condensation products of ethylene oxide, propylene glycol and propylene oxide produced by the Wyandotte Chemical Corporation. Pluronics 1-64, for instance, is a liquid with a hydrophobic base having a molecular weight of approximately 1750; 40% of the molecule, by weight, consisting of hydrophilic polyoxyethylene groups, and the remaining 60% hydrophobic polypropylene groups. The molecular structure of this class of materials can be represented as:

(H3 preferably where m, the polyoxypropylene constituent has an average value from about to 30 and (C H O) n+n, the polyoxyethylene constituents, equal about 20 to 60 percent of the total weight of the compound. Mixed polyether glycols of this type are described in U.S. Patent No. 2,674,619 which also describes a method for their preparation.

The amount of surface-active agent which is provided in the water bank may vary within :wide limits and the wide ranges of solubility of such agents in water for example, enables a wide selection of proportions to be made. Advantageously, the amount of surface-active agent injected is that sufficient to effect arrival, for instance of at least about 20 parts per million, of the surface-active agent in the migrating water bank at the producing Well. Us ually there is no need to use other than relatively small amounts in the water bank as, for example, from a few thousandths of a percent up to higher amounts. Upper amounts may be about 2% and higher, but large amounts are costly and thus I prefer that the water bank contain about 10 to 100 ppm. of the surfactant upon arrival at or in the vicinity of the output well.

In the preferred method of practicing the invention, a concentrated solution of the surface-active agent is injected into the bore of an input well. The surfactant injection is preferably followed with a straight water injection to move the surfactant solution out from the immediate combustion area. in porous formations this can be accomplished by injection of inert gases or other fluids. A burner of the type, for instance, described in application Serial No. 97,142, filed June 4, 1949, in the names of John I. Piros and Oliver P. Campbell is then installed in the input well at formation level and ignited. Hydrocarbon fuel, conveniently natural gas or a crude oil is burned with an oxygen-containing gas such as air at high temperature either on the surface, or preferably within the hole. Alternatively, other means such as chemical igniters and fuels may be employed to establish ignition of the oil-bearing formation. Usually, the fuel-air mixture is proportioned to provide a temperature within the range of about 700 to 00 F. A sufficient period of pre-heating is provided to heat a substantial portion of the rock formation surrounding the wvell bore to a tcniperaure above the ignition temperature for hydrocarbons in the formation, i.e. above about 450 to 500 F. to about 1500 F. or more. After the oil-bearing stratum around the well bore for a radius of several feet has been heated to a high temperature, preferably above 1000 F, combustion in the well bore is terminated. The heated zone is now moved into the formation, for instance, by injecting unheated, non-combustible gas such as combustion gases, air or air containing an amount of fuel gas below the explosive limit. Alternatively, air and fuel gas may be injected alternately in a manner preventing burning the well bore. Alternatively, fuel gas containing an oxygen content below the rich explosive limit may be used for movement of the heated zone into the formation. The gases enter the well bore cold and pick up preheat from the rock face. By transfer of heat outwardly through the rock the heated zone is moved away from the well bore. Once the Well bore has been cooled below the ignition point a heat wave is established lWhiCll can be propagated within the formation. An oxygen-containing gas drive is then employed to propagate the heat wave, advantageously air at as high an input rate as practicable taking into account the permeability of the rock, power requirements for compression and pressure limitations. The input rate and partial pressure of oxygen are maintained in any event high enough to insure combustion of hydrocarbon residues in the rock as the oil is released and moved out into the formation before the advancing heat wave. if the residue is too lean to provide sutficient heat to maintain the peak temperature of the advancing wave at a high level, e.g. generally about 700 to 1500 F., fuel gas may be injected with the injected air. The injected gas progresses radially out into the formation from the input well and is preheated to above the ignition temperature as it passes through the peak temperature zone. As the preheated air comes into contact with residual fuel at the leading edge of the wave, the in-situ combustion process is continued, generating additional heat and thus propagating the heat wave in the form of an advancing annular ring. The resulting combustion gases under elevated pressure are forced into the porous oil-bearing stratum for a length of time sufficient to raise the temperature of a large body of sand surrounding the well to a temperature below the fusion temperature of the rock but Well above the ignition temperature of the residual carbon. In propagating the wave the free oxygen content of the injected gases is suficient to maintain combustion and will usually be in the range of about 1 to 25 Kb, preferably about '5 to 20%.

In another embodiment of the present invention, the surface active agent can be incorporated directly into the water bank as it migrates toward the output well. This can be done, for example, by first locating the water bank, drilling into the water bank and incorporating the surfactant as a concentrate in water or in slug form. The location of the water bank can be determined by the usual geological observations of core samples, test bores, etc.

The following example is included to further illustrate the invention.

In a well spacing of 2 /2 acres per in ection well wherein the oil-bearing formation has a sand thickness of '10 feet, a porosity of 20% and a water saturation of 25%, the following procedure is followed:

29.5 barrels of a 1% concentration of Pluronic L-64 in water is injected into the input wet. The surfactant is then displaced into the formation with barrels of water. A burner is installed in the input well at the formation level and ignited. A hydrocarbon fuel is burned with air within the input well, the fuel-air mixture being proportioned to establish a heat wave having a temperature of about 1000 F. The heat wave is then propagated through the 2% acres to a producing well by injecting air.

At the time of arrival of the Water bank at the proclucing well, the water bank consists of approximately 14,75 0 barrels of water (9,750 barrels of formation water plus 5,000 barrels of combustion Water). The average surfactant concentration in this water bank is approximately 20 parts per million.

The surfactant addition lowers the quantity of oil left behind by the Water bank by about 30%. A corresponding 30% decrease in the oxygen required to propagate the Wave through the formation is found. The decrease is calculated by comparing the MM 0.1". per acre foot of air usually required to propagate the heat wave in the formation to the MM of. per acre foot of air employed when the surface-active agent is used.

I claim:

1. In the recovery of oil from an oil-bearing underground formation wherein combustion is established within the formation, an oxygen-containing propagating gas is injected into the formation through an input well whereby said combustion is propagated toward an output Well and a water bank is formed ahead of said combustion as a result thereof, the step which comprises providing in said water bank in said formation subsequently traversed 2 by said combustion a water-miscible, surface-active agent in an amount sufficient to decrease the oxygen required in said propagating gas to move the combustion through the formation.

2. The method of claim 1 wherein the surface-active agent is oil-immiscible.

3. The method of claim 2 wherein the water bank contains about 10 to parts per million of said surfaceactive agent.

4. The method of claim 1 wherein the surface active agent is non-ionic.

5. In the recovery of oil from an oil-bearing underground formation wherein combustion is established Within the formation, an oxygen-containing propagating gas is injected into the formation through an input well to propagate said combustion toward an output Well and a water bank is for-med ahead of said combustion as a result thereof, the step which comprises injecting into said formation adjacent an input well a water-miscible surface active agent prior to establishment of said combustion, the amount of said surface active agent being sufficient to decrease the oxygen required in said propagating gas to move the combustion through the formation.

References Cited in the file of this patent UNITED STATES PATENTS 2,788,071 Pelzer Apr. 9, 1957 2,812,817 Sayre Nov. 12, 1957 2,875,831 Martin et al. Mar. 3, 1959 OTHER REFERENCES Breston, J. N.: Recovering Oil by Fire Flooding, Monitor, July-August, 1958. 

1. IN THE RECOVERY OF OIL FROM AN OIL-BEARING UNDERGROUND FORMATION WHEREIN COMBUSTION IS ESTABLISHED WITHIN THE FORMATION, AN OXYGEN-CONTAINING PROPAGATING GAS IS INJECTED INTO THE FORMATION THROGH AN INPUT WELL WHEREBY SAID COMBUSTION IS PROPAGATED TOWARD AN OUTPUT WELL AND A WATER BANK IS FORMED AHEAD OF SAID COMBUSTION AS A RESULT THEREOF, THE STEP WHICH COMPRISES PROVIDING IN SAID WATER BANK IN SAID FORMATION SUBSEQUENTLY TRAVERSED BY SAID COMBUSTION A WATER-MISCIBLE, SURFACE-ACTIVE AGENT IN AN AMOUNT SUFFICIENT TO DECREASE THE OXYGEN REQUIRED IN SAID PROPAGATING GAS TO MOVE THE COMBUSTION THROUGH THE FORMATION. 